Why do two photos shot at ISO 160 and ISO 1600 look almost the same?
Asked 6/3/2012
2 views
2 answers
0
I shot two images on a Nikon D7000 and expected the ISO 1600 photo to look much worse than the ISO 160 photo, but they appear very similar. One was taken at ISO 160, f/22, 8 seconds, and the other at ISO 1600, f/4, 1/40 second, both around 39mm equivalent focal length.
Why don’t I see a big quality difference, and what differences should I normally expect between ISO 160 and ISO 1600?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
5
I'm adding this as a second answer as it is probably the fundamental issue involved.
Apples <> Pears
The two pictures have fundamentally different conditions and cannot be fairly compared.
The ISO 160 picture contains 30 times more sensor noise than it should have for a fair comparison.
What I and others have said in the other answers all has relevance, but -
1600 ISO settings were f/4, 1/40s
160 ISO settings were f/22, 8 seconds.
Assuming starting at ISO 1600 (either way works)
If exposure time had been decreased when ISO was decreased then the change would have been:
- f/4, 1/40s to f/4, 1/4s
ie ISO ratio = 1600/160 = 10
exposure ratio = (1/40) / (1/4) = 10
BUT at the same time, aperture was changed from f/4 to f/22
This necessitated an increase in exposure time by a factor of apertures-squared (as f number is a measure of diameter but light input is related to area which is proportional to diameter squared.
So exposure time had to be increased by a furher ratio of (22/4) squared
= a further 30.25 times !!!
So the ISO 160 picture contains 30 times more sensor noise than it should have for a fair comparison.
This still does not explain the actual content differences in the images.
Originally by user6263. Source · Licensed CC BY-SA 4.0
user6263
14y ago
0
Generated from our catalog & community — verify before relying on it.
You’re not making a like-for-like comparison. ISO changed, but so did aperture and shutter speed by a lot, so these photos were made under very different conditions.
The main difference ISO usually introduces is more visible noise and often less dynamic range at higher settings. In your samples, there is some extra grain/noise in the darker area of the ISO 1600 image, but it’s fairly subtle.
Why it looks subtle:
- The D7000’s sensor is known for very good high-ISO performance.
- ISO 1600 is not especially extreme on a modern camera.
- Bright, colorful areas hide noise better than smooth dark tones.
- Your ISO 160 shot used a very small aperture (f/22) and a much longer exposure, so it isn’t an equal test of ISO alone.
If you want to compare ISO properly, keep the scene, aperture, framing, and exposure level the same, changing only ISO and shutter speed to compensate. For example, compare shots at the same aperture and equivalent exposure. Then look closely at shadows and smooth gradients, where higher ISO noise is easiest to see.
Recommended products
UniqueBot
AI14y ago
Your Answer
Related Questions
For Milky Way shots, is a shorter exposure at higher ISO better than a longer exposure at lower ISO?
If ISO stays the same, how do aperture and shutter changes affect a photo with the same exposure?
Why am I getting pink or purple bands in long-exposure photos on my Nikon D7100?
Why do streetlights leave squiggly light trails in a long-exposure photo, and how can I avoid them?
Does changing film ISO on a Lomography Spinner 360 change the effective f-stop the right way around?